Structure of a self-splicing group II intron catalytic effector domain 5: Parallels with spliceosomal U6 RNA

NMR spectra showing the chemical shift perturbations of D5 nucleotides on binding MgCl₂ in the N1, N3, N7, and N9 aromatic region. Arrows depict residues with the most chemical shift perturbation with increasing magnesium ion concentration (0 and 10 mM), indicative of a likely ion-binding site. Residues in the triad region (A2 and G3) and the bulge (A24) are boxed. Note how A2’s N7, but not N9 nor N3, is selectively perturbed and A24’s N3, but not N1, is selectively perturbed. G3 is not perturbed at the N7 or N9 positions.